The present invention relates to new internal mold release compositions which increase the gel time of reaction mixtures, thereby enabling large molds to be filled easier via the Structural Reaction Injection Molding (i.e. SRIM) process.
SRIM processes for the production of molded parts having enhanced flexural modules are increasing in importance in the automotive industry, etc. There are, however, numerous problems associated with the use of a reinforcing mat in the SRIM process. These problems include displacement of the mat in the mold, incomplete filling of the mold, and part distortion. It is believed that some of the problems are due to the RIM reactants reaching too high a viscosity in too short a time to allow the mat to be completely impregnated with the reaction mixture.
One solution to this problem was described in U.S. Pat. No. 4,435,349. This patent describes the use of a reaction mixture of a polyisocyanate, with a polyol having an equivalent weight of above 500, a relatively low molecular weight chain extender, and a delayed action catalyst. The working examples of the patent use an excess of polyol having an equivalent weight of over 1800 and a molecular weight of no less than about 5500.
U.S. Pat. No. Re. 33,609 described another solution to some of the problems associated with SRIM processes. The reaction mixture used in this patent comprises an organic polyisocyanate with a specific polyol blend. The specific polyol blend comprises at least one polyether polyol having a hydroxy functionality of from 2 to 8 and a molecular weight of from 350 to below 1100, at least one hydroxyl functional material containing from 2 to 8 hydroxyl groups and having a molecular weight of below 350, and no more than 45% by weight, based on the total weight of the polyol component, of an active hydrogen containing compound having a molecular weight of 1800 or more. However, this systems described by this patent are relatively fast in terms of gel times and reactivities. Accordingly, these systems are not suitable for filling large molds.
U.S. Pat. No. 4,868,224 relates to a system that provides easy release from a bare metal mold. This system utilizes a zinc carboxylate in the B-side of the reaction mixture. However, one problem with this system is that the zinc carboxylate/solubilizer combination catalyzes the hydroxyl/isocyanate reaction. This makes the system relatively fast in terms of gel times, thereby leading to problems in filling large molds.
Another IMR composition for use in flexible foam systems is described in U.S. Pat. No. 4,876,019. These IMR compositions comprise: (A) at least one metal salt of an organic compound derived from a compound containing at least one carboxylic acid group, phosphorus containing acid groups, or boron containing acid groups or mixtures thereof, wherein the organic material contains a backbone of siloxane chains or at least one terminal or pendant saturated or unsaturated aliphatic hydrocarbon chain containing at least about 7 carbon atoms; (B) a compound containing at least one primary amine group and/or at least one secondary amine group per molecule or mixtures thereof; and, optionally, (C) at least one organic compound containing at least one carboxylic acid group, phosphorus containing acid groups, or boron containing acid groups or mixtures thereof, wherein the organic compound contains a backbone of siloxane chains or at least one terminal or pendant saturated or unsaturated aliphatic hydrocarbon chain containing at least about 7 carbon atoms.
When attempting to fill large molds, the rate at which these fast reacting systems need to be injected is too high for most equipment throughout the industry. Another problem commonly associated with a high injection rate is the disturbance of the reinforcement at the injection port.
One solution to this problem of systems exhibiting fast reactivity, is to use a prepolymer of an isocyanate with a fatty acid. U.S. Pat. No. 5,019,317 describes one such system based on an isocyanate prepolymer. However, prepolymers are very expensive. Accordingly, this type of system is not always economically feasible due to the increased production costs.
The present invention is directed to a method of filling large molds using the Structural Reaction Injection Molding process. This is based on extending the gel time of isocyanate-based systems, without reducing the catalyst needed for the proper curing of the urethane. Prepolymers are not necessary in the present invention. A reduction in the reactivity of the reaction mixture is achieved through the addition of a fatty acid to the B-side. The present invention reduces production costs, delays the gel time of the system, and allows full catalysis of the urethane to take place.